Loctite 638 and 641 are bearing retainers, and probably too viscous to do the capillary action thing you are looking for.
A thin cyanoacrylate adhesive is probably best - dob some onto some scrap plastic, pick the adhesive up with a toothpick, and use the toothpick to deliver the adhesive - rather than trying to deliver it from the spout of the bottle, where it can end up everywhere.
And don't use accelerator on it, although it speeds things up, it can compromise the integrity of the bond.
Before applying the adhesive I'd give the part a dousing / agitation (and repeat) in isopropyl alcohol beforehand, to try and ensure that the fissure is as clean as possible . If you are able to submerge it in isopropyl alcohol in an ultrasonic tank, and then dry it using compressed air, that would be ideal.